This proposal presents projects in two closely related areas. The first is a magnetic circular dichroism (MCD) and absorption spectroscopy study of porphyrins whose peripheral substituents (-CH=CH2, -COOH, -CHO, -COCH3, -CN), either alone or in concert, cause an inversion of the normal sign pattern in their MCD spectra. The second set of projects utilizes the electronic consequences of these effects to probe porphyrin polypeptide steric interactions in the pocket of heme proteins. Our proposition for the first group of projects is that the MCD and, comcomitantly, the absorption spectrum of any substituted porphyrin or chlorin - regardless of the number, kind, or relative orientations of the substituents - can be predicted provided only that the MCD and absorption spectra of a fairly limited set of disubsituted porphyrins is known. We propose to synthesize the required sets of disubstituted porphyrins and to measure their spectra as free-bases and as complexed with a limited number of metal ions. We will use this data set in conjunction with some theoretical work to establish symmetry rules for predicting spectra. We will then test these predictions on an entirely different set of porphyrins. In the second group of projects we will reconstitute apomyoglobin and apohemoglobin with some formyl- (and acetyl-) vinyl substituted deuterohemes. These porphyrins will have inverted MCD bands. The intensities of these MCD bands is directly related to the overlap of the substituents' orbitals with those of the porphyrin ring and thus to the amount of steric interaction felt by the porphyrin in the heme pocket. We will use a series of model compounds to provide a basis for quantitating this interaction in several spin-states of the oxidized and reduced artifical heme proteins. Quantitation will be based on modeling by CNDO calculations. We will also investigate the spin-state changes induced in artifical hemoglobins by the allosteric effector, inositol hexaphosphate.